Micro-optic film materials projecting synthetic images generally comprise (a) a light-transmitting polymeric substrate, (b) an arrangement of micro-sized image icons located on or within the polymeric substrate, and (c) an arrangement of focusing elements (e.g., microlenses). The image icon and focusing element arrangements are configured such that when the arrangement of image icons is viewed through the arrangement of focusing elements, one or more synthetic images are projected. These projected images may show a number of different optical effects.
Material constructions capable of presenting such effects are described in U.S. Pat. No. 7,333,268 to Steenblik et al., U.S. Pat. No. 7,468,842 to Steenblik et al., U.S. Pat. No. 7,738,175 to Steenblik et al., U.S. Pat. No. 7,830,627 to Commander et al., U.S. Pat. No. 8,149,511 to Kaule et al.; U.S. Patent Application Publication No. 2010/0177094 to Kaule et al.; U.S. Patent Application Publication No. 2010/0182221 to Kaule et al.; European Patent No. 2162294 to Kaule et al.; and European Patent Application No. 08759342.2 (or European Publication No. 2164713) to Kaule et al.
These film materials may be used as security devices for authentication of banknotes, secure documents and products. For banknotes and secure documents, these materials are typically used in the form of a strip or thread and either partially embedded within the banknote or document, or applied to a surface thereof. For passports or other identification (ID) documents, these materials could be used as a full laminate or embedded as an anti-counterfeit feature in polycarbonate passports.
The prior art film materials described above, which are known as moiré magnifiers, generally start with a two-dimensional (2D) array of identical image icons. They may, however, also start with image icons that are altered or modulated in ways that provide different effects such as changing images or images that slowly rotate, etc. For three-dimensional (3D) effects, these film materials are constructed using a “bottom-up” approach in the sense that the view of a static object from the perspective of each individual lens is calculated spatially from a model of a static 3D object, and the corresponding icon is generated from the collection of the lens' views. Using this approach, each icon is calculated individually based on the static model of the 3D object. The approach has at least the following limitations:                (a) The finished synthetic image is only a static 3D object;        (b) The finished synthetic image will have a “snap” in the field of view; and        (c) The finished synthetic image is limited to a palette of at most one color, and furthermore one tone of that color. It is a binary image, and does not have any shading or grayscale.        
The term “snap”, which will be described in more detail below, constitutes a large discontinuity in what the observer sees when the observer moves outside of the device's range (but within its field of view) and looks at the device.
The drawbacks noted above are addressed by exemplary embodiments of the present invention, which use a “top-down” approach in the sense that each desired complete synthetic image as seen by an observer from all given viewpoints is defined, and then each of these individual images (which is different from spatial information) that correspond to the different viewpoints is processed and then used to define a part of what each lens sees. The sum total of all of these viewpoint images will ultimately define a significant portion of the image plane that would normally contain only icons (“image layer”). This approach will allow for the following major improvements over the prior art:                (a) The finished synthetic image can be, among other things: a moving 3D object; a dynamic (morphing or transforming) 3D object; a dynamic design of curves, abstract designs, shapes, photographs, 3D objects and images;        (b) The finished synthetic image can be designed such that there is no “snap” in the field of view;        (c) The finished synthetic images can include “halftone” effects similar to grayscale dithering. Furthermore, this method will help enable the coordination of several layers to ultimately produce synthetic images that incorporate full color dynamic designs and 3D images; and        (d) The finished synthetic images do not have to be sourced from models of 3D objects. The synthetic images can originate from any type of digital image (e.g., photographs, drawings, mathematical plots and curves, etc.).        
The present invention specifically provides a security device for projecting a collection of synthetic images, which comprises: a collection of focusing elements, with each focusing element having an optical footprint; and at least one image layer, the focusing elements and image layer(s) together projecting a different image as the device is viewed at different angles,
wherein, the image layer(s) is made up of an array of discrete digitized domains, each domain constituting an identical or substantially identical subset of each focusing element's optical footprint, the domains being discrete in that no two subsets overlap and every point in each subset is closest to its respective focusing element, each domain being divided into a number of discrete pixels equal to the number of images,
wherein, each image is processed digitally, the number of pixels in each digitally processed image being equal or proportionate to the total number of focusing elements, the pixels in each digitally processed image being distributed to the same location within each digitized domain, such that each location within one digitized domain is marked with the color of a pixel from a different digitally processed image, allowing for the device to project a different image as the device is viewed at different angles.
In the following write-up, the inventive device is described as a device that projects synthetic images which are seen by an observer. There is a correspondence between the location of the observer relative to the device and the synthetic image that the observer sees from any particular viewpoint. For example, the synthetic images may represent different viewpoints of a target object or image that change from one viewpoint image to another viewpoint image as the location of the observer changes relative to the device. The nature of each synthetic image can, however, be completely arbitrary, much like the images that are provided by a display device such as a television or computer monitor. Moreover, in an exemplary embodiment, a special symmetry is used to generate the synthetic images, which allows the device to be manufactured without regard for registration, which is a known problem with prior art devices.
In contrast to a moiré magnifier, which has an array of more or less ‘continuous’ images, an exemplary embodiment of the image layer(s) in the security device of the present invention is a binary grid of distributed digital images where each pixel in the grid is either “on or off” (i.e., colored or uncolored).
In a first exemplary embodiment, the inventive security device projects a collection of grayscale or halftone synthetic images. In this embodiment, grayscale is implemented using grayscale images with reduced color palettes (e.g., four shades of gray) and focusing element clustering (i.e., a cluster of focusing elements instead of one focusing element is used for each viewpoint image-pixel).
In a second exemplary embodiment, the inventive security device projects a collection of 3D synthetic images. In this embodiment, the viewpoint images are related in such a way that an observer sees at least two different 2D images at one time, which produce binocular stereopsis perception of the images in the observer.
In a third exemplary embodiment, the inventive security device projects a collection of synthetic images that have no snap. More specifically, each distributed viewpoint image is a composite viewpoint image prepared by using one or more continuous mathematical scalar functions to define or alter a quantifiable parameter in the viewpoint image.
The present invention further provides a computer-implemented method for producing a security device for projecting a collection of synthetic images, wherein the security device is made up of a collection of focusing elements in the form of a focusing element sheet, each focusing element having an optical footprint; and at least one image layer, the focusing elements and image layer(s) together projecting a different viewpoint image as the device is viewed at different angles, the method comprising:                (a) forming the image layer(s) by:                    (i) compiling a collection of different raw viewpoint images with each raw viewpoint image prescribing what an observer should see when viewing the security device from a given angle;            (ii) choosing a domain for each focusing element in the focusing element sheet, and arranging the domains in the form of a grid on or within the image layer(s), the domains constituting identical subsets of each of the focusing element's optical footprints such that no two subsets overlap and every point in each subset is closest to its respective focusing element once the image layer(s) is placed in a focal plane of the collection of focusing elements, wherein exact registration between the domains and the focusing elements is not required;            (iii) digitizing each chosen domain by dividing each domain into a number of discrete pixels, which will each represent a portion of a different viewpoint image, the number of pixels in each digitized domain being equal to the number of different viewpoint images, the digitized domains forming a raster grid;            (iv) digitally processing each of the different raw viewpoint images to form binary images, wherein the number of pixels in each digitally processed viewpoint image is equal to (or proportionate to) the total number of focusing elements in the focusing element sheet that will be used to represent the desired complete image;            (v) distributing the collection of different processed viewpoint images into the raster grid by marking each digitized domain pixel with the color of the corresponding viewpoint image pixel through a process called ‘distribution’, which involves assigning an address to each pixel in each digitized domain, and then assigning one image to each pixel having the same address in each digitized domain, such that each location within one digitized domain will be marked with the color of a pixel from a different processed viewpoint image; and                        (b) placing the formed image layer(s) in a focal plane of the focusing element sheet.        
Also provided by way of the present invention is a security device prepared in accordance with this method.
In a first exemplary embodiment, the inventive method produces a security device that projects a collection of grayscale or halftone synthetic images. More specifically, the “compiling” step when forming the image layer(s) of the inventive method is directed toward a collection of different raw grayscale or halftone viewpoint images, while the “processing” step involves modifying the raw viewpoint images by reducing the number of shades of gray in each image's color palette, optionally dithering the remaining shades of gray in each image's color palette, and then representing each such processed viewpoint image as a finished binary image. After distributing the collection of different finished binary images into the raster grid, the inventive method in this first exemplary embodiment further comprises using a cluster of focusing elements (e.g., a 2×2 cluster of lenses) for each viewpoint image-pixel.
In a second exemplary embodiment, the inventive method produces a security device that projects a collection of 3D synthetic images. More specifically, the “compiling” step when forming the image layer(s) of the inventive method involves modeling an object in a 3D-graphics rendering program and obtaining different raw viewpoint images of the object by rendering views of the object using a (virtual or real) camera at multiple positions, a one-to-one correspondence existing between the number of views rendered by the camera and the number of pixels in each digitized domain.
In a third exemplary embodiment, the inventive method produces a security device that projects a collection of synthetic images that have no snap. More specifically, the inventive method further comprises: determining mathematical scalar functions of x and y that are continuous; applying one or more such mathematical scalar functions to copies of the domain to obtain one or more scalar values, the domain constituting a region on the xy plane that has been repeated in a spatially periodic sense; and using the one or more scalar values to define or alter a quantifiable parameter in the collection of viewpoint images distributed to the domains, thereby generating composite viewpoint images.
The present invention further provides sheet materials and base platforms that are made from or employ the inventive security device, as well as documents made from these materials. The term “documents”, as used herein designates documents of any kind having financial value, such as banknotes or currency, and the like, or identity documents, such as passports, ID cards, driving licenses, and the like, or other documents, such as tags or labels. The inventive security device is also contemplated for use with consumer goods as well as bags or packaging used with consumer goods, such as potato chip bags.
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.